The discovery was announced late Monday in a peer-reviewed paper released early by the journal Proceedings of the National Academy of Sciences. The laser scanning shows a previously undocumented formal urban planned landscape integrating the 1,200 year old temples.

It’s all obscured by dense forest.

Study lead author Damien Evans of the University of Sydney tells The Age of Australia in a video that it was a Eureka moment when the airborne lasers revealed the sudden and immediate picture of an entire city, with urban temples.

The airborne lasers also indicated that the civilization there eventually collapsed because of deforestation and broken reservoir systems.